Whichever cylinder the clean spark plug came out of is probably the cylinder taking coolant. Note the borescope photo of that cylinder is one of the missing from your collection.
I think myself and others already suggest pulling the head. It’s probably going to have to be tested by Magnaflux or Ziglo to find the crack if it isn’t a gasket problem.This rationale suggests that if I do a leak down test on that cylinder, it will ALSO need to be performed at operating temp. I am already imagining trying to find TDC on #5 and then plugging the tester finagling around the scalding block and headers. Seems like it would be easier to just pull the damn head off and just look for any sign of trouble.
Are you indicating that the gasket and the intake don’t cover the port roof? If so that is an air leak.There is no doubt at this point that I will be tearing into this engine in short order. But I did notice another oddity and wanted to ask yall about it. Check out this gap between the intake manifold and intake port on cylinder 1. And yes, that's a feeler gauge on the second picture buried in there. It's a 0.015 gap. Wouldn't this create a big vacuum leak? At least for cylinder one?
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